init: use SO_BINDTODEVICE instead of temp address for DHCP

Replace the temporary link-local address (169.254.1.1) workaround with
SO_BINDTODEVICE.

The temp address caused the kernel to use 169.254.1.1 as the source IP in DHCP
packets; gvproxy then tried to reply to that address and failed with
"no route to host". With this change the source IP should be 0.0.0.0, which is
what RFC 2131 requires for DHCPDISCOVER.

Signed-off-by: Matej Hrica <mhrica@redhat.com>

Author: mtjhrc

init/dhcp.c

@@ -291,20 +291,6 @@ int do_dhcp(const char *iface)
         goto cleanup;
     }
 
-    /* Temporary link-local address and route avoid the need for raw sockets */
-    struct in_addr temp_addr;
-    inet_pton(AF_INET, "169.254.1.1", &temp_addr);
-    struct in_addr temp_gw = {.s_addr = INADDR_ANY};
-
-    if (mod_route4(nl_sock, iface_index, RTM_NEWROUTE, temp_gw) != 0) {
-        printf("couldn't add temporary route\n");
-        goto cleanup;
-    }
-    if (mod_addr4(nl_sock, iface_index, RTM_NEWADDR, temp_addr, 16) != 0) {
-        printf("couldn't add temporary address\n");
-        goto cleanup;
-    }
-
     /* Send request (DHCPDISCOVER) */
     sock = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
     if (sock < 0) {
@@ -319,6 +305,12 @@ int do_dhcp(const char *iface)
         goto cleanup;
     }
 
+    if (setsockopt(sock, SOL_SOCKET, SO_BINDTODEVICE, iface,
+                   strlen(iface) + 1) < 0) {
+        perror("setsockopt SO_BINDTODEVICE failed");
+        goto cleanup;
+    }
+
     /* Bind to port 68 (DHCP client) */
     memset(&bind_addr, 0, sizeof(bind_addr));
     bind_addr.sin_family = AF_INET;
@@ -476,16 +468,6 @@ int do_dhcp(const char *iface)
         /* Calculate prefix length from netmask */
         unsigned char prefix_len = count_leading_ones(ntohl(netmask.s_addr));
 
-        /* Drop temporary address and route, configure what we got instead */
-        if (mod_route4(nl_sock, iface_index, RTM_DELROUTE, temp_gw) != 0) {
-            printf("couldn't remove temporary route\n");
-            goto cleanup;
-        }
-        if (mod_addr4(nl_sock, iface_index, RTM_DELADDR, temp_addr, 16) != 0) {
-            printf("couldn't remove temporary address\n");
-            goto cleanup;
-        }
-
         if (mod_addr4(nl_sock, iface_index, RTM_NEWADDR, addr, prefix_len) !=
             0) {
             printf("couldn't add the address provided by the DHCP server\n");
@@ -496,16 +478,7 @@ int do_dhcp(const char *iface)
                 "couldn't add the default route provided by the DHCP server\n");
             goto cleanup;
         }
-
         set_mtu(nl_sock, iface_index, mtu);
-    } else {
-        /* Clean up: we're clearly too cool for IPv4 */
-        if (mod_route4(nl_sock, iface_index, RTM_DELROUTE, temp_gw) != 0) {
-            printf("couldn't remove temporary route\n");
-        }
-        if (mod_addr4(nl_sock, iface_index, RTM_DELADDR, temp_addr, 16) != 0) {
-            printf("couldn't remove temporary address\n");
-        }
     }
 
     ret = 0;